The present invention relates to an arrangement for a covering element made from an at least partially transparent base material, which comprises an integrated electro-chromatic layer for electrical control of the light transmission through the covering element.
It is previously known, in different connections, to design glass sheets and other transparent covering elements with electro-chromatic layers, by means of which the light transmission through the glass sheet can be controlled. In this connection the electro-chromatic layer usually comprises two electrically conductive layers, which surround on both sides an ionically conductive layer. By means of exposing the ionically conductive layer, via the electrically conductive layers, to different electrical voltage fields, the light transmission can be controlled through the ionically conductive layer and thus through the whole covering element also. The electrical voltage necessary for the control is usually obtained from a per se conventional voltage source. According to what is stated, for example, in the American patent specification U.S. Pat. No. 4,240,021 which relates to a solar-cell powered clock, a battery can also be used as a voltage source. In this case, inside the electro-chromatic layer, a number of photocells are arranged, which convert the light incident on them into electrical power in order to charge a battery. Since the electro-chromatic layer is arranged outside the photocells, it is possible to control the light incident on the photocells and thus control the electrical power emitted from the photocells. This is used in order to prevent overloading of the battery which is connected to the photocells.
As far as vehicles are concerned, use has been made of electro-chromatic layers in windscreens and other covering elements only in certain prototype cars. The intention in this case is among other things to be able, in sunny weather, to prevent too much sunlight shining into an area to be irradiated by the sunlight, such as, the interior space of the vehicle and thus the associated increase in temperature. This can, however, principally be used during operation of the vehicle when sufficient power is obtained from the generator of the vehicle. The possibilities of preventing an increase in the temperature of the interior space during a long parking time, for example, are limited by the power which is stored in the battery of the vehicle. If parking continues for too long, there is a risk that the battery will be discharged and that as a result of this the vehicle cannot be started.